What is Relay

what is relay 29

[otw_is sidebar=otw-sidebar-1]What is Relay,Basics of relay,relay symbol,types of relayIn this post I will discuss about the Basics of relay and Types of Relay. In the previous posts I have discussed the simulation of important sensors in Proteus and this post will be oriented around Relay Module simulation in Proteus.

After reading this post the reader will be able to learn about the basics of the Relay Module, electronic circuit of the Relay Module, simulation model of the Relay Module and the simulation of Relay Module with Arduino in Proteus. The reader will also learn about how to interface the Arduino with Relay Module. So sit back, keep reading and enjoy learning.you can see how to relay interfacing with arduino UNO in proteus.  my last new post is nodemcu esp8266 library for proteus



WHAT IS Relay:

A relay is electromagnetic switch. It is used in applications to turn on and off an circuit by a lower power signal, or where several circuits must b controlled by one signal.A module can be defined as the system or circuit which is designed to perform the particular task and is layout as a plug and play device. Because of the large market due to students and hobbyists the companies have designed a lot of modular circuits. For example the Wi-Fi module, Bluetooth Module, Stepper motor driver, LED driver, motor driver are just a few modular systems. So a relay module is the modular system which compliance the relays and the necessary circuit to drive that relay. The relay module either consists of one relay or multiple relays. So in short the relay module is the circuit that consists of the relays and is used in switching applications. The relay modules commonly available in the market are as shown in the following image:

What is Relay,types of relay,symbol of relay,relay diagram

As shown in the above image that the Relay Modules are available in different packages that is containing different amount of Relays on board. The user can select any relay module according to his/her requirement.

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Circuit for Relay Module:

Now let us discuss the circuit that the Relay module is composed but before going into the discussion of circuit configuration let us learn about the pin configuration of the Relay.

The above image describes the pin configuration of the 12 volt, 5 pin relay. Other types of relays with different voltage requirement and pinout are also available but you will see the one described above is the most common type of relay. As can be seen in the above image that the relay consists of the 5 pins, one pin is common pin which is common between the normally connected and normally open pins. The other two pins are the power supply pins of the coil which energizes the coil and magnetizes the contacts.

The circuit for the relay module that drives the relay is as shown in the following image:

Circuit for Relay Module,relay circuit diagram



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Relay Operation

A relay is electromagnetic switch. It is used in applications to turn on and off an circuit by a lower power signal, or where several circuits must b controlled by one signal.


Main parts in a relay

  1. Electromagnet
  2. Moveable armature
  3. Switch points contacts
  4. Spring


  How does Relay work.

There are two circuits CONTROL CIRCUIT and LOAD CIRCUIT.

When the control switch is turned ON current starts flowing through a coil, it generates magnetic field that attracts the armature and the load circuit is closed.

Thus is Normally Open (NO) relay – contact is open when the relay is not energized.

Other type is Normally Closed (NC)– contact is closed when the relay is not energized

Types of Relay

Relays can be used to control several circuits by one signal. A relay switches one or more poles, each of whose con tacts can be thrown by energizing the coil. There are different types of relays:

types of relay,Basics of relay

SPST– Single Pole Single Throw

SPDT– Single Pole Double Throw

DPST– Double Pole Single  Throw

DPDT– Double Pole Double Throw


 SPST- Single Pole Single Throw Relay.

These have two terminals which can be connected or disconnected. Including two for the coil, such a relay has four terminals in total.


SPDT- Single Pole Double Relay

Throw.  A common terminal connects to either of two others. Including two for the coil,  such a relay has five terminals in total.


 DPST- Double Pole Single Throw Relay.

These have two pairs of terminals. Equivalent to two SPST switches or relays actuated by a single coil. Including two for the coil, such a relay has six terminals in total.


DPDT- Double Pole Double Throw Relay

.  These have two rows of change-over terminals. Equivalent to two SPDT switches or relays actuated by a single coil.  Such a relay has eight terminals, including the coil.



The “S” or “D” may be replaced with a number, indicating multiple switches connected to a single actuator. For example, 4PDT indicates a four pole double throw relay that has 12 switch terminals.

Relay Symbol

RELAY SYMBOL,types of relay

Application of Relay

Relays are used wherever it is necessary to control a high power or high voltage circuit with a low power circuit, especially when galvanic isolation is desirable.

The first application of relays was in long telegraph lines, where the weak signal received at an intermediate station could control a contact, regenerating the signal for further transmission.

High voltage or high current devices can be controlled with small, low voltage wiring and pilot switches. Operators can be isolated from the high voltage circuit. Low power devices such as microprocessors can drive relays to control electrical loads beyond their direct drive capability.

In an automobile, a starter relay allows the high current of the cranking motor to be controlled with small wiring and contacts in the ignition key.

An electromagmetic relay was presented . Nowadays there is another type of relay- Solid State Relay which uses power semiconductors such as thyristors and transistors, to switch currents up to around a hundred amperes. Solid state relays have fast switching speeds compared with electromagnetic relays, and have no physical contacts to wear out.

Basics of relay

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Electromagnetic relays are still commonly used in applications because they are simple, cheap and most important provide complete physical isolation between control and load circuit so in applications where a circuit must be completely on or off with minimal on-state voltage drop, or to avoid danger of injury or damage from leakage current the electromagnetic relay is the better choice.

i hope my tutorial Basics of relay is helpfull for you

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